Proposals have been made in the past to provide a pumping system which would automatically sense the presence of liquid and then pump the sensed liquid from one location to another. Such a pump could be used in draining sumps or pumping from a well.
One typical device, which has been in use for years is the combining of an air-driven double diaphragm pump and a pneumatic bubbler/air valve. For example, this kind of system is available from Air Pump Company of Grand Blanc, Mich., USA and is sold under the trademark APCO.
Systems of these types require the use of a double diaphragm pump, these pumps being generally larger than 10 inches in diameter. The double diaphragm pump is used to draw under vacuum fluids from one location and push them to another. This type of system is limited since it can only draw fluid up under a vacuum from about 25 feet depth. To reach greater depths, the pump must be lowered into a rather large well, sump or opening. Additionally, the nature of the double diaphragm pump's mechanical action makes it an inefficient pump to use.
Another type of system utilizes internal controls to operate pneumatic valves and pressurize and exhaust the pump based upon the fullness of the pump. An example of such a system is shown in U.S. Pat. No. 4,467,831 to French, issued Aug. 28, 1984.
This system utilizes a displacer to load and unload spring-loaded opposing poppets and thus cause the pump body to pressurize and exhaust. These types of systems have several inherent defects which make the use of the system fraught with maintenance and control problems. A displacer weight, spring tension and friction acting on upper and lower poppets which seat in O-rings must be maintained in balance. Too much pressure on either the lower or the upper poppet can cause the poppet to jam into the O-ring and "freeze" the pump. If the pressure is not great enough on the upper poppet, the spring tension can lift it off its seat and cause air to constantly stream into the pump and out its exhaust.
In practice the pressure range in which this design can operate when the pump must operate within a 4-inch well casing or smaller spans about 40 psi. If the pressure to be used falls or rises outside of this range, the internal mechanism of the pump must be adjusted to accommodate such operation or the pump will fail to operate. This can be a severe problem if the pressure to the pump fluctuates or the head against which the fluid is being pumped increases.
In addition, when the pump is introducing pressurized air into the pump chamber to push out fluid, some of this air bleeds off out the exhaust. This causes a loss of energy. If the pump is constructed so that fluid enters through a check valve at the base of the pump, a fast influx of fluid can remove weight from the displacer and cause the poppets to shift. When this happens, pressurized air forces the fluid out of the pump, moving the displacer down and reseating the poppets. This action is repeated rapidly and a "stuttering" or "quick cycle" is developed. When this condition is reached, the pump rate and efficiency decreases dramatically.
In addition, the friction of the O-rings against the poppets can change if the chemicals which are being pumped cause the O-rings to become lubricated or swell. This can cause the valve mechanism to shift too soon or not at all. This design is also adversely affected by the flow of fluid into and out of the pump. Such flow creates drag on the displacer and causes premature opening and closing of air valves. This can cause a stuttering-type of failure.
Another type of system is generally described in U.S. Pat. No. 5,004,405 issued to Breslin on Apr. 2, 1991 entitled PNEUMATICALLY POWERED SUBMERSIBLE FLUIDS PUMPS WITH INTEGRATED CONTROLS. One example is that pump manufactured by Clean Environment Equipment of Oakland, Calif. and sold under the trademark AutoPump. Essentially the same pump is also manufactured by QED of Ann Arbor, Mich. and Ejector Systems in Addison, Ill.
These types of systems utilize a moving float inside the pump which travels with the fluid in the pump. When the pump is full, the float and the fluid are at their uppermost point of travel and the buoyant float forces a control rod upwards, causing a pneumatic valve to switch. The pneumatic valve allows pressurized air into the pump, forcing the water out. When the pump is empty, the float and the fluid are at their lowermost point in the pump. As the fluid level decreases, the float pulls the same control rod downwards, shifting the pneumatic valve to exhaust the pump and allow it to fill again.
This pump design works well. However, the float is an expensive part of the pump and is contained inside the pump casing. When the float is inside the pump casing, it occupies space and thus eliminates volume which might otherwise be used for pumping.